Note 9 - Stockholders' Equity - Dividend Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Per share amount (in dollars per share)	$ 0.28	$ 0.22	$ 0.18
Quarterly Dividends 1 [Member]
Record date	Mar. 22, 2018	Mar. 22, 2017
Payment date	Apr. 05, 2018	Apr. 06, 2017
Per share amount (in dollars per share)	$ 0.07	$ 0.055
Dividend payment	$ 1,351	$ 1,029
Quarterly Dividends 2 [Member]
Record date	May 22, 2018	May 24, 2017
Payment date	Jun. 07, 2018	Jun. 08, 2017
Per share amount (in dollars per share)	$ 0.07	$ 0.055
Dividend payment	$ 1,353	$ 1,036
Quarterly Dividends 3 [Member]
Record date	Aug. 22, 2018	Aug. 23, 2017
Payment date	Sep. 06, 2018	Sep. 06, 2017
Per share amount (in dollars per share)	$ 0.07	$ 0.055
Dividend payment	$ 1,369	$ 1,055
Quarterly Dividends 4 [Member]
Record date	Nov. 20, 2018	Nov. 22, 2017
Payment date	Dec. 06, 2018	Dec. 07, 2017
Per share amount (in dollars per share)	$ 0.07	$ 0.055
Dividend payment	$ 1,372	$ 1,060

Aggregate dividends declared during the period for each share of common stock outstanding.

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